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Re: Describing Images (and similar), and Descriptor discovery.

From: Toby Inkster <tai@g5n.co.uk>
Date: Wed, 9 Jun 2010 15:16:46 +0100
To: nathan@webr3.org
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-ID: <20100609151646.25d5f675@miranda.g5n.co.uk>
On Wed, 09 Jun 2010 14:01:32 +0100
Nathan <nathan@webr3.org> wrote:

> I'm just wondering what approaches people are taking to describing
> non rdf/html resources, such as Images, PDFs and similar?

As Michael pointed out, if you consider the RDF document to be a
"representation" (in HTTP terminology) of the image, then you can serve
both the binary image and the RDF from the same URI using conneg.

However, usually an RDF description of an image would considered a
separate resource from the image itself. (They're likely to have
different dc:created dates, and possibly different dc:creators too.) In
this case, they should have separate URIs. For example:

	http://example.com/image (the image)
	http://example.com/describe?uri=http://example.com/image (RDF)

Or:

	http://example.com/image (the image)
	http://example.com/image,about (RDF)

So, now that we're serving the image and the RDF as different
resources, it becomes a question of how to discover the RDF data given
the image's URI. The Web Linking Internet Draft provides a way forward.

	http://tools.ietf.org/html/draft-nottingham-http-link-header-10

HTTP responses to requests for the image itself would include the
following HTTP header (line-wrapped for legibility):

	Link: </image,about>;
		rel="describedby";
		type="application/rdf+xml"

The Web Linking draft is due to become an RFC Real Soon Now, and
hopefully once that happens, linked data clients will start adding
transparent support for it.

-- 
Toby A Inkster
<mailto:mail@tobyinkster.co.uk>
<http://tobyinkster.co.uk>
Received on Wednesday, 9 June 2010 14:18:23 UTC

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